Optical display with fluted optical plate

ABSTRACT

A display system has a light source, a display panel and an arrangement of light management layers disposed between the light source and the display panel. The light source illuminates the display panel through the arrangement of light management layers. The arrangement of light management layers includes a fluted plate that has a front layer facing the display panel, a back layer facing the light source, and a plurality of connecting members connecting the front and back layers. In some embodiments the fluted plate includes a first light management layer, a cross member substantially parallel to, and spaced apart from, the first light management layer, and an arrangement of first connecting members connecting the cross member and the first light management layer.

FIELD OF THE INVENTION

The invention relates to optical displays, and more particularly todisplay systems that are illuminated from behind, such as may be used inLCD monitors and LCD televisions.

BACKGROUND

Liquid crystal displays (LCDs) are optical displays used in devices suchas laptop computers, hand-held calculators, digital watches andtelevisions. Some LCDs include a light source that is located to theside of the display, with a light guide positioned to guide the lightfrom the light source to the back of the LCD panel. Other LCDs, forexample some LCD monitors and LCD televisions (LCD-TVs), are directlyilluminated using a number of light sources positioned behind the LCDpanel. This arrangement is increasingly common with larger displays,because the light power requirements, to achieve a certain level ofdisplay brightness, increase with the square of the display size,whereas the space available for locating light sources along the side ofthe display only increases linearly with display size. In addition, someLCD applications, such as LCD-TVs, require that the display be brightenough to be viewed from a greater distance than other applications, andthe viewing angle requirements for LCD-TVs are generally different fromthose for LCD monitors and hand-held devices.

Some LCD monitors and most LCD-TVs are commonly illuminated from behindby a number of cold cathode fluorescent lamps (CCFLs). These lightsources are linear and stretch across the full width of the display,with the result that the back of the display is illuminated by a seriesof bright stripes separated by darker regions. Such an illuminationprofile is not desirable, and so a diffuser plate is used to smooth theillumination profile at the back of the LCD device.

Currently, LCD-TV diffuser plates employ a polymeric matrix ofpolymethyl methacrylate (PMMA), poly(carbonate), cycloolefins, randomcopolymers of polymethylmethacrylate or polystyrene, combined with avariety of dispersed phases that include glass, polystyrene beads, andCaCO₃ particles. These plates often deform or warp after exposure to theelevated temperatures of the lamps. In addition, some diffusion platesare provided with a diffusion characteristic that varies spatiallyacross its width, in an attempt to make the illumination profile at theback of the LCD panel more uniform. Such non-uniform diffusers aresometimes referred to as printed pattern diffusers. They are expensiveto manufacture, and increase manufacturing costs, since the diffusingpattern must be registered to the illumination source at the time ofassembly. In addition, the diffusion plates require customized extrusioncompounding to distribute the diffusing particles uniformly throughoutthe polymer matrix, which further increases costs.

Furthermore, to prevent warping or other types of physical distortions,the diffuser plate has to be of a minimum thickness relative to itsheight and width. As the size of the display increases, this means thatthe diffuser plate also becomes increasingly thick, thus increasing theweight of the display.

SUMMARY OF THE INVENTION

One embodiment of the invention is directed to a display system that hasa light source, a display panel, and an arrangement of light managementlayers disposed between the light source and the display panel. Thelight source illuminates the display panel through the arrangement oflight management layers. The arrangement of light management layersincludes a fluted plate that has a front layer facing the display panel,a back layer facing the light source, and a plurality of connectingmembers connecting the front and back layers.

Another embodiment of the invention is directed to a light managementunit that includes a fluted layer. The fluted layer has a first lightmanagement layer, a cross member substantially parallel to, and spacedapart from, the first light management layer and an arrangement of firstconnecting members connecting the cross member to the first lightmanagement layer.

These and other aspects of the present application will be apparent fromthe detailed description below. In no event, however, should the abovesummaries be construed as limitations on the claimed subject matter,which subject matter is defined solely by the attached claims, as may beamended during prosecution.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be more completely understood in consideration of thefollowing detailed description of various embodiments of the inventionin connection with the accompanying drawings, in which like referencenumerals designate like elements, and wherein:

FIG. 1 schematically illustrates a display device that uses a flutedplate;

FIG. 2A schematically illustrates a fluted plate;

FIGS. 2B and 2C schematically illustrate fluted plates with attachedoptical films;

FIG. 3 schematically illustrates a fluted plate having a spatiallyvariable single pass transmission;

FIG. 4 schematically illustrates a fluted plate having a spatiallyvariable refractive index;

FIGS. 5A and 5B schematically illustrate fluted plates whose upper andlower layers have respectively spatially varying thicknesses;

FIGS. 6A and 6B schematically illustrate fluted plates whose upper andlower layers have respectively spatially varying thicknesses;

FIGS. 7A and 7B schematically illustrate fluted plates having flutes ofdifferent cross-sectional shape;

FIG. 8A schematically illustrates a top view of a fluted plate showingflutes arranged parallel;

FIG. 8B schematically illustrates a top view of a fluted plate showingsets of parallel flutes arranged perpendicularly;

FIGS. 9 and 10 schematically illustrate fluted plates with opticallyuseful surface structure;

FIGS. 11A, 11B, 12A and 12B schematically illustrate various opticalfilm arrangements that include a fluted plate;

FIGS. 13A and 13B schematically illustrate the construction of a flutedplate using a spine attached to an optical film;

FIGS. 14A and 14B schematically illustrate the construction of a flutedplate using a double-sided spine attached to optical films;

FIGS. 15 and 16 schematically illustrate different film arrangementsbuilt around a double-sided spine;

FIG. 17 schematically illustrates the construction of a fluted plateusing first and second layers having interconnecting members; and

FIG. 18 schematically illustrates a display system having a heattransfer medium flow through flutes of the fluted plate.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION

The present invention is applicable to liquid crystal displays (LCDs, orLC displays), and is applicable to LCDs that are directly illuminatedfrom behind and to LCDs that are edge lit, for example, LCDs used in LCDmonitors and LCD televisions (LCD-TVs).

The diffuser plates currently used in LCD-TVs are based on a polymericmatrix, for example polymethyl methacrylate (PMMA), polycarbonate (PC),or cyclo-olefins, formed as a rigid sheet. The sheet contains diffusingparticles, for example, organic particles, inorganic particles or voids(bubbles). These plates often deform or warp after exposure to theelevated temperatures of the light sources used to illuminate thedisplay. These plates also are more expensive to manufacture and toassemble in the final display device.

The present application discloses directly illuminated LCD devices thathave an arrangement of light management layers positioned between theLCD panel itself and the light source. The arrangement of lightmanagement layers can include a diffuser layer whose transmission andhaze levels are designed to provide a direct-lit LC display whosebrightness is relatively uniform across the display.

A schematic exploded view of an exemplary direct-lit LC display device100 is presented in FIG. 1. Such a display device 100 may be used, forexample, in an LCD monitor or LCD-TV. The display device 100 is based onthe use of an LC panel 102, which typically comprises a layer of LC 104disposed between panel plates 106. The plates 106 are often formed ofglass, and may include electrode structures and alignment layers ontheir inner surfaces for controlling the orientation of the liquidcrystals in the LC layer 104. The electrode structures are commonlyarranged so as to define LC panel pixels, areas of the LC layer wherethe orientation of the liquid crystals can be controlled independentlyof adjacent areas. A color filter may also be included with one or moreof the plates 106 for imposing color on the image displayed.

An upper absorbing polarizer 108 is positioned above the LC layer 104and a lower absorbing polarizer 110 is positioned below the LC layer104. In the illustrated embodiment, the upper and lower absorbingpolarizers are located outside the LC panel 102. The absorbingpolarizers 108, 110 and the LC panel 102 in combination control thetransmission of light from the backlight 112 through the display 100 tothe viewer. In some LC displays, the absorbing polarizers 108, 110 maybe arranged with their transmission axes perpendicular. When a pixel ofthe LC layer 104 is not activated, it may not change the polarization oflight passing therethrough. Accordingly, light that passes through thelower absorbing polarizer 110 is absorbed by the upper absorbingpolarizer 108, when the absorbing polarizers 108, 110 are alignedperpendicularly. When the pixel is activated, on the other, hand, thepolarization of the light passing therethrough is rotated, so that atleast some of the light that is transmitted through the lower absorbingpolarizer 110 is also transmitted through the upper absorbing polarizer108. Selective activation of the different pixels of the LC layer 104,for example by a controller 114, results in the light passing out of thedisplay at certain desired locations, thus forming an image seen by theviewer. The controller may include, for example, a computer or atelevision controller that receives and displays television images. Oneor more optional layers 109 may be provided over the upper absorbingpolarizer 108, for example to provide mechanical and/or environmentalprotection to the display surface. In one exemplary embodiment, thelayer 109 may include a hardcoat over the absorbing polarizer 108.

It will be appreciated that some type of LC displays may operate in amanner different from that described above. For example, the absorbingpolarizers may be aligned parallel and the LC panel may rotate thepolarization of the light when in an unactivated state. Regardless, thebasic structure of such displays remains similar to that describedabove.

The backlight 112 includes a number of light sources 116 that generatethe light that illuminates the LC panel 102. Linear, cold cathode,fluorescent tubes, that extend across the display device 100, arecommonly used as the light sources 116 in the display device 100. Othertypes of light sources may be used, however, such as filament or arclamps, light emitting diodes (LEDs), lasers, flat fluorescent panels orexternal fluorescent lamps. This list of light sources is not intendedto be limiting or exhaustive, but only exemplary.

The backlight 112 may also include a reflector 118 for reflecting lightpropagating downwards from the light sources 116, in a direction awayfrom the LC panel 102. The reflector 118 may also be useful forrecycling light within the display device 100, as is explained below.The reflector 118 may be a specular reflector or may be a diffusereflector. One example of a specular reflector that may be used as thereflector 118 is Vikuiti™ Enhanced Specular Reflection (ESR) filmavailable from 3M Company, St. Paul, Minn. Examples of suitable diffusereflectors include polymers, such as polyethylene terephthalate (PET),polycarbonate (PC), polypropylene, polystyrene and the like, loaded withdiffusely reflective particles, such as titanium dioxide, bariumsulphate, calcium carbonate and the like. Other examples of diffusereflectors, including microporous materials and fibril-containingmaterials, are discussed in U.S. Pat. No. 6,780,355 (Kretman et al.),incorporated herein by reference.

An arrangement 120 of light management layers is positioned between thebacklight 112 and the LC panel 102. The light management layers affectthe light propagating from backlight 112 so as to improve the operationof the display device 100. For example, an arrangement 120 of lightmanagement layers may include a diffuser layer 122. The diffuser layer122 is used to diffuse the light received from the light sources, whichresults in an increase in the uniformity of the illumination lightincident on the LC panel 102. Consequently, this results in an imageperceived by the viewer that is more uniformly bright. The diffuserlayer 122 may include bulk diffusing particles distributed throughoutthe layer, or may include one or more surface diffusing structures, or acombination thereof.

The arrangement of light management layers 120 may also include a gaindiffuser, a layer that diffuses light generally in the viewingdirection. In some embodiments a gain diffuser contains transparentparticles that protrude from the surface of the film, thus providingoptical power to light that passes through the particles. This reducesthe divergence of the light, resulting in an increase in on-axisbrightness, sometimes refered to as gain. Some types of gain diffusersare described in greater detail in U.S. Pat. No. 6,572,961 (Koyama etal.), incorporated herein by reference.

The arrangement 120 of light management layers may also include areflective polarizer 124. The light sources 116 typically produceunpolarized light but the lower absorbing polarizer 110 only transmits asingle polarization state, and so about half of the light generated bythe light sources 116 is not transmitted through to the LC layer 104.The reflective polarizer 124, however, may be used to reflect the lightthat would otherwise be absorbed in the lower absorbing polarizer, andso this light may be recycled by reflection between the reflectivepolarizer 124 and the reflector 118. At least some of the lightreflected by the reflective polarizer 124 may be depolarized, andsubsequently returned to the reflective polarizer 124 in a polarizationstate that is transmitted through the reflective polarizer 124 and thelower absorbing polarizer 110 to the LC layer 104. In this manner, thereflective polarizer 124 may be used to increase the fraction of lightemitted by the light sources 116 that reaches the LC layer 104, and sothe image produced by the display device 100 is brighter.

Any suitable type of reflective polarizer may be used, for example,multilayer optical film (MOF) reflective polarizers; diffuselyreflective polarizing film (DRPF), such as continuous/disperse phasepolarizers, wire grid reflective polarizers or cholesteric reflectivepolarizers.

Both the MOF and continuous/disperse phase reflective polarizers rely onthe difference in refractive index between at least two materials,usually polymeric materials, to selectively reflect light of onepolarization state while transmitting light in an orthogonalpolarization state. Some examples of MOF reflective polarizers aredescribed in co-owned U.S. Pat. No. 5,882,774 (Jonza et al.),incorporated herein by reference. Commercially available examples of MOFreflective polarizers include Vikuiti™ DBEF-D200 and DBEF-D440multilayer reflective polarizers that include diffusive surfaces,available from 3M Company, St. Paul, Minn.

Examples of suitable DRPF include continuous/disperse phase reflectivepolarizers as described in co-owned U.S. Pat. No. 5,825,543 (Ouderkirket al.), incorporated herein by reference, and diffusely reflectingmultilayer polarizers as described in e.g. co-owned U.S. Pat. No.5,867,316 (Carlson et al.), also incorporated herein by reference. Othersuitable types of DRPF are described in U.S. Pat. No. 5,751,388(Larson).

Some examples of suitable wire grid polarizers include those describedin U.S. Pat. No. 6,122,103 (Perkins et al.). Wire grid polarizers arecommercially available from, inter alia, Moxtek Inc., Orem, Utah.

Some examples of suitable cholesteric polarizers include those describedin, for example, U.S. Pat. No. 5,793,456 (Broer et al.), and U.S. Pat.No. 6,917,399 (Pekorny et al.). Cholesteric polarizers are oftenprovided along with a quarter wave retarding layer on the output side,so that the light transmitted through the cholesteric polarizer isconverted to linear polarization.

The arrangement 120 of light management layers may also include abrightness enhancing layer 128. A brightness enhancing layer is one thatincludes a surface structure that redirects off-axis light in adirection closer to the axis of the display. This increases the amountof light propagating on-axis through the LC layer 104, thus increasingthe brightness of the image seen by the viewer. One example is aprismatic brightness enhancing layer, which has a number of prismaticridges that redirect the illumination light, through refraction andreflection. Examples of prismatic brightness enhancing layers that maybe used in the display device include the Vikuiti™ BEFII and BEFIIIfamily of prismatic films available from 3M Company, St. Paul, Minn.,including BEFII 90/24, BEFII 90/50, BEFIIIM 90/50, and BEFIIIT.

The arrangement 120 of light management layers may also include asupport layer 130, which may be used for providing support to the otherlight management layers. In some arrangements, one of the other lightmanagement layers may be integrated with the support layer 130. Forexample, some existing televisions include diffusing particles in arelatively thick (2-3 mm), rigid polymer sheet, thus combining thefunctions of providing support and optical diffusion into a singlelayer.

Support layer 130 advantageously includes a fluted plate, which is aplate that includes flutes, or spaces, between the two surfaces of theplate. A cross-sectional view of an exemplary fluted plate 200 isschematically illustrated in FIG. 2A. The fluted plate 200 includes afirst layer 202 and a second layer 204, with connecting members 206connecting the first and second layers 202, 204. The open spaces 208surrounded by the connecting members 206 and the first and second layers202, 204 may be considered to be flutes.

The fluted plate 200 is self-supporting and may, in some exemplaryembodiments, be used to provide support to other light managementlayers. The fluted plate 200 may be made of any suitable material, forexample organic materials such as polymers. For example, the flutedplate 200 may be formed using any suitable method, for exampleextrusion, molding, and the like.

The thickness of the fluted plate 200 and the size of the flutes 208 maybe selected depending on the particular application. For example, thefluted plate may be a few mm thick, for example in the range ofapproximately 1 mm-4 mm, or may be thicker. The fluted plate 200 mayalso be thinner, for example having a thickness of approximately 50 μmor more. Also, the center-to-center spacing of the flutes 208 may beselected to be any suitable value. For example, the spacing may be inthe range of about 1-4 mm, or greater. In other embodiments, the flutespacing may be less, for example down to around 50 μm or less.

The use of a fluted plate may reduce the weight of a display system suchas a television. For example, in a 40 inch LCD-TV, a conventional soliddiffuser plate typically weighs about 2.3 lbs (1 kg), and accounts forabout 5% of the overall weight of the television. A fluted plate weighsonly a fraction of a comparable solid plate, commonly about 25%, and soa fluted plate would provide only about 1% of the overall weight of thetelevision.

In addition, the fluted plate has the mechanical advantages of an“I-beam” with upper and lower plates separated by an air space and aconnecting member. Accordingly, the fluted plate provides highresistance to warping and curling under the high illumination conditionstypical in many display systems.

The directions of the flutes may be oriented in a desired direction withrespect to the light sources. For example, if the light sources areelongated, as with most fluorescent lamps, the flutes may be oriented tobe parallel to the light sources, or may be oriented to be not parallel.A specific orientation between the light sources and the flutes, for agiven design of light source and fluted plate, may provide improvedillumination uniformity and also improved thermal response, e.g. warp,curl, etc.

Suitable polymer materials for the fluted plate may be amorphous orsemi-crystalline, and may include homopolymer, copolymer or blendsthereof. Polymer foams may also be used. Example polymer materialsinclude, but are not limited to: amorphous polymers such aspoly(carbonate) (PC); poly(styrene) (PS); acrylates, for example acrylicsheets as supplied under the ACRYLITE® brand by Cyro Industries,Rockaway, N.J.; acrylic copolymers such as isooctyl acrylate/acrylicacid; poly(methylmethacrylate) (PMMA); PMMA copolymers; cycloolefins;cylcoolefin copolymers; acrylonitrile butadiene styrene (ABS); styreneacrylonitrile copolymers (SAN); epoxies; poly(vinylcyclohexane);PMMA/poly(vinylfluoride) blends; atactic poly(propylene); poly(phenyleneoxide) alloys; styrenic block copolymers; polyimide; polysulfone;poly(vinyl chloride); poly(dimethyl siloxane) (PDMS); polyurethanes;poly(carbonate)/aliphatic PET blends; and semicrystalline polymers suchas poly(ethylene) (PE); poly(propylene) (PP); olefin copolymers, such asPP/PE copolymers; poly(ethylene terephthalate) (PET); poly(ethylenenaphthalate)(PEN); polyamide; ionomers; vinyl acetate/polyethylenecopolymers; cellulose acetate; cellulose acetate butyrate;fluoropolymers; poly(styrene)-poly(ethylene) copolymers; PET and PENcopolymers; and blends that include one or more of the polymers listed.

Some exemplary embodiments of the fluted plate 200 include polymermaterials that are substantially transparent to light. Some otherexemplary embodiments may include diffusive material in the fluted plate200 using, for example, a polymer matrix containing diffusing particles.The polymer matrix may be any suitable type of polymer that issubstantially transparent to visible light, for example any of thepolymer materials listed above.

The diffusing particles may be any type of particle useful for diffusinglight, for example transparent particles whose refractive index isdifferent from the surrounding polymer matrix, diffusely reflectiveparticles, or voids or bubbles in the matrix. Examples of suitabletransparent particles include solid or hollow inorganic particles, forexample glass beads or glass shells, solid or hollow polymericparticles, for example solid polymeric spheres or polymeric hollowshells. Examples of suitable diffusely reflecting particles includeparticles or beads of PS, PMMA, polysiloxane, titanium dioxide (TiO₂),calcium carbonate (CaCO₃), barium sulphate (BaSO₄), magnesium sulphate(MgSO₄) and the like. In addition, voids in the polymer matrix may beused for diffusing the light. Such voids may be filled with a gas, forexample air or carbon dioxide.

Other additives may be provided to the fluted plate. For example, thefluted plate may include antioxidants, such as Irganox 1010 availablefrom Ciba Specialty Chemicals, Tarrytown, N.Y. Other examples ofadditives may include one or more of the following: an anti-weatheringagent, UV absorbers, a hindered amine light stabilizer, a dispersant, alubricant, an anti-static agent, a pigment or dye, a nucleating agent, aflame retardant, a blowing agent, or nanoparticles.

The entire fluted plate 200 may be formed from diffusing material orselected portions of the fluted plate 200 may be made of diffusingmaterial. For example, the first layer 202, or the second layer 204, maybe formed of diffusing material while the remainder of the plate 200 isformed of some other material. In other embodiments, both the first andsecond layers 202, 204 may be formed of diffusing material. When afluted plate 200 formed of a diffusive material is used in a displaysystem, such as is exemplified in FIG. 1, the fluted plate providesmechanical support as well as providing a diffusing function, so that aseparate diffuser layer may be omitted.

In other exemplary embodiments, the fluted plate 200 may be providedwith a diffuser layer 210, for example as schematically illustrated inFIG. 2B. The diffuser layer 210 may be attached to either the firstlayer 202 or the second layer 204. In addition, in some embodiments,there may be diffuser layers attached to each of the first and secondlayers 202, 204. The diffuser layer 210 may be attached to the flutedplate 200 using an adhesive layer (not shown) or, in other embodiments,the diffuser layer 210 may itself be an adhesive layer attached to thefluted plate 200.

Commercially available materials suitable for use in a diffusing layerinclude 3M™ Scotchcal™ Diffuser Film, type 3635-70 and 3635-30, and 3MT™Scotchcal™ ElectroCut™ Graphic Film, type 7725-314, available from 3MCompany, St. Paul, Minn. Other commercially available diffusers includeacrylic foam tapes, such as 3M™ VHB™ Acrylic Foam Tape No. 4920.

In some exemplary embodiments, the diffuser layer 210 has a diffusioncharacteristic that is uniform across its width, in other words theamount of diffusion experienced by light is the same for points acrossthe width of the diffuser layer 210.

The diffuser layer 210 may optionally be patterned, or supplemented withor replaced by an optional patterned diffuser 210 a. The optionalpatterned diffuser 210 a may include, for example, a patterned diffusingsurface or a printed layer of diffuser, such as particles of titaniumdioxide (TiO₂). The patterned diffuser 210 a may lie on the diffuserlayer 210, between the diffuser layer 210 and the fluted plate 200. Inaddition, a patterned diffuser may be applied to a fluted plate 200 thatis formed, at least partially, of diffusing material.

The fluted plate 200 may be provided with protection from ultraviolet(UV) light, for example by including UV absorbing material or materialthat is resistant to the effects of UV light. Suitable UV absorbingcompounds are available commercially, including, e.g., Cyasorb™ UV-1164,available from Cytec Technology Corporation of Wilmington, Del., andTinuvin™ 1577, available from Ciba Specialty Chemicals of Tarrytown,N.Y. The fluted plate 200 may also include brightness enhancingphosphors that convert UV light into visible light.

Other materials may be included into the layers of the fluted plate 200to reduce the adverse effects of UV light. One example of such amaterial is a hindered amine light stabilizing composition (HALS).Generally, the most useful HALS are those derived from a tetramethylpiperidine, and those that can be considered polymeric tertiary amines.Suitable HALS compositions are available commercially, for example,under the “Tinuvin” tradename from Ciba Specialty Chemicals Corporationof Tarrytown, N.Y. One such useful HALS composition is Tinuvin 622. UVabsorbing materials and HALS are further described in U.S. Pat. No.6,613,819 (Johnson et al.), incorporated herein by reference.

In other embodiments, the fluted plate 200 may have two diffuser layers210, 212 attached respectively to the first and second layers 202, 204of the fluted plate 200. The diffuser layers 210, 212 may each beapplied directly to the respective layer 202, 204 of the fluted plate200, as is illustrated in FIG. 2C, or may be attached using a layer ofadhesive (not shown).

The two diffuser layers 210, 212 may have the same diffusion properties,or may have different diffusing properties. For example, the diffuserlayer 210 may possess a different transmission or haze level from thesecond diffuser layer 212, or may be of a different thickness.

The optical properties of the fluted plate may be uniform across itswidth, but this is not necessary. In some exemplary embodiments, forexample the fluted plate 300 shown in FIG. 3, the amount of diffusionimparted by the fluted plate 300 itself may spatially vary across thewidth of the plate 300. This may be achieved, for example, byintroducing bulk diffusing particles nonuniformly across an extrudedfluted plate. The graph above the fluted plate shows a spatial variationin the single pass transmission, T. The single pass transmission is thefraction of incident light that is transmitted through the fluted plate300: higher levels of transmission indicate less diffusion and lowerlevels of transmission indicate more diffusion. In the illustratedexample, the periodicity in the spatial variation of the transmission isequal to the separation distance between the connecting members 306.Such a spatial variation in the diffusion may be useful for reducingnonuniformities in the brightness of the transmitted light due to theconnecting members 306. There is no requirement, however, that thevariation in T have this periodicity, and the variation in T may havesome other periodicity, or need not be periodic.

Another optical characteristic of the fluted plate that may vary acrossthe fluted plate 400 is the refractive index of one or both of the firstand second layers 402, 404, as is schematically illustrated in FIG. 4.Such a variation may be achieved, for example, by introducing a materialof a different refractive index nonuniformly across an extruded flutedplate. The graph above the fluted plate 400 shows a spatial variation inthe refractive index. In the illustrated example, the periodicity in thespatial variation of the refractive index is equal to the separationdistance between the connecting members 406. Such a spatial variation inthe diffusion may be useful for reducing nonuniformities in thebrightness of the transmitted light due to the connecting members 406.There is no requirement, however, that the variation in the refractiveindex have this periodicity, and the variation in the refractive indexmay have some other periodicity, or need not be periodic.

In some exemplary embodiments, one or more of the layers of the flutedplate may have a thickness that varies across the plate. For example, inthe fluted plate 500 schematically illustrated in FIG. 5A, the thicknessof the first layer 502 varies from being relatively thin at the edges ofthe plate 500 to relatively thick at the center of the plate 500, whilethe second layer 504 maintains a constant thickness across its width. Avariation in the thickness of the first layer 502 may be used, interalia, to provide additional strength to the plate or to provide avariation in the optical characteristics of the plate. In anillustrative example, where the first layer 502 contains a uniformconcentration of bulk diffusive particles, a variation in the thicknessof the first layer 502 may be used to provide a spatially varyingdiffusive characteristic. In the illustrated example, there is greaterdiffusion of the light passing through the center portion of the plate500 than at the edge.

In other embodiments, the second layer 504, or both the first and secondlayers 502, 504 may have a variable thickness. For example, asillustrated in FIG. 5B, a fluted plate 520 has a first layer 522 ofuniform thickness and a second layer 524 of variable thickness. It willbe appreciated that variations in the thickness of the first and/or thesecond layer 502, 504, 522, 524 may be periodic or non-periodic.

In some embodiments, the surfaces of the material surrounding the spacesor flutes may be parallel or perpendicular to the outer surfaces of thefluted plate, but this is not a necessary condition. In some exemplaryembodiments, the surfaces of the first or second layer defining theflutes may be non-parallel to the upper surface of the fluted plate.This is schematically illustrated in FIG. 6A for one particular flutedplate 600, in which the lower surface 602 a of the first layer 602 isnon-parallel to the upper surface 604 b of the second layer 604, atleast for some of the flutes 608. Consequently, the cross-sectionalshapes of some of the flutes 608 a are not square or rectangular.

The lower surface of the flute may also be non-parallel to the lowersurface of the second layer. For example, in the embodiment of FIG. 6B,the thicknesses of both the first and second layers 622, 624 are notuniform over the width of the plate 620. In other exemplary embodiments,the first layer may be uniformly thick while only the second plate has anon-uniform thickness.

The flutes need not be quadrilateral in shape, and may take on othershapes. For example, in one exemplary embodiment schematicallyillustrated in FIG. 7A, the fluted plate 700 has triangle-shapedconnecting members 706 connecting between the first and second layers702, 704. Consequently, the flutes 708 have a triangle cross-sectionalso. In another exemplary embodiment, schematically illustrated in FIG.7B, the fluted plate 720 has upper and lower layers 722, 724 that havesinusoidal inner surfaces 722 a, 724 a defining the flutes 728. Theconnecting members 726 are formed where the sinusoidal surfacescoincide.

In another exemplary embodiment, schematically illustrated in FIG. 7C,the fluted plate 730 has upper and lower layers 732, 734 that areconnected together via curved connecting members 736. In the illustratedembodiment, the curved connecting members 736 alternate between curvingin one direction and the opposite direction, to produce a corrugatedeffect.

Many different cross-sections may be used for the connecting members andthe flutes, in addition to those illustrated herein. Further, theillustrated embodiments are presented for purposes of illustration only,and there is no intention to limit the scope of the invention only tothose cross-sections illustrated herein.

In some exemplary embodiments, for example the fluted plate 800schematically illustrated in FIG. 8A which shows a top view of the plate800, the flutes 808 are linear and arranged parallel to each other. Inother exemplary embodiments, for example the fluted plate 820schematically illustrated in FIG. 8B, the flutes 828 are linear but arearranged with a first group of flutes parallel to each other and asecond group of flutes 828 parallel to each other but perpendicular tothe first group. In other embodiments, different flutes may lie atdifferent angles to each other.

In some embodiments, the surface of the first or second layers may beflat, and provided with an anti-reflection coating. In otherembodiments, the first and/or the second layer may provide some opticalfunction. For example, the outer or inner surface of the first and/orsecond layers may be provided with a matte finish. In another exemplaryembodiment, the first and second layers may be provided with somesurface structure. For example, the fluted plate 900 schematicallyillustrated in FIG. 9 has first and second layers 902, 904 attachedtogether via connecting members 906. In this particular embodiment, theupper surface 910 of the first layer 902 is provided with a series ofprismatic ribs 912. The ribs 912 may lie parallel to each other, inwhich case the surface 910 operates like a prismatic brightnessenhancing layer, redirecting some off-axis light, exemplified by lightray 914, to propagate in a direction more parallel to the axis 916.

The fluted plate may have other types of surfaces. In another example,schematically illustrated in FIG. 10, the first layer 1002 of the flutedplate 1000 has an upper surface 1010 that comprises a series of lenses1012 that provide optical power to the light 1014 passing through theplate. The lenses 1012 may, but are not required to, have a width equalto the spacing between the connecting members 1006. The lenses 1012 maybe lenticular lenses, stretching across the width of the plate 1000.This type of lens is particularly well suited to a plate manufacturedusing an extrusion process. Other methods may be used to form the lenses1012, such as molding.

The fluted plate may be used for supporting other optical layers in adisplay. For example, one or more other layers may be attached to thefluted plate. The following examples are presented to illustrate somepossible combinations of other layers with a fluted plate. FIG. 11Ashows an arrangement 1100 of optical layers, having a fluted plate 1101with a reflective polarizer layer 1110 attached to the upper surface ofan upper layer 1102 of the fluted plate. The reflective polarizer layer1110 may be attached using an adhesive, for example a clear adhesive oran optically diffusing adhesive. A prismatic brightness enhancing layer1112 may be attached above the reflecting polarizer layer 1110. In someexemplary embodiments, it may be desirable for at least some of thelight to enter the brightness enhancing layer 1112 through an airinterface or an interface going from a low to a high refractive index.Therefore, a layer of low index material, for example a fluorinatedpolymer, may be placed between the brightness enhancing layer 1112 andthe next layer below the brightness enhancing layer 1112.

In other exemplary embodiments, an air gap may be provided between thebrightness enhancing layer 1112 and the layer below the brightnessenhancing layer 1112. One approach to providing the air gap is toinclude a structure on one or both of the opposing faces of thebrightness enhancing layer 1112 and the layer below the brightnessenhancing layer 1112. In the illustrated embodiment, the lower surface1114 of the brightness enhancing layer 1112 is structured withprotrusions 1116 that contact the adjacent layer layer. Voids 1118 arethus formed between the protrusions 1116, with the result that lightentering into the brightness enhancing layer 1112 at a position betweenthe protrusions 1116 does so through an air interface. In otherembodiments, the reflecting polarizer layer 1110 may be omitted and theprismatic brightness enhancing layer 1112 attached directly to thefluted plate 1101. In some embodiments, the fluted layer 1101 mayprovide optical diffusion, or a separate diffusing layer may beprovided, for example attached to a lower layer 1104 of the fluted layer1101 or attached to the first layer 1102 of the fluted layer 1101,between (i) the fluted layer and (ii) the reflective polarizer layer1110 and/or the prismatic brightness enhancing layer 1112.

Other approaches to forming voids, and thus providing an air interfaceto light entering the brightness enhancing layer, may be used. Forexample, the brightness enhancing layer may have a flat lower surface,with the adjacent layer being structured with protrusions. These, andadditional approaches, are discussed in U.S. Patent Publication No.2003/0223216 A1 (Emmons et al.), incorporated herein by reference. Anyof the embodiments of a fluted plate discussed herein may be adapted toprovide an air interface for light entering the brightness enhancinglayer.

The order of the films attached to the fluted plate 1101 may bedifferent. For example, a reflective polarizer layer 1110 may beattached to the prismatic surface of the brightness enhancing layer1112, and the brightness enhancing layer 1112 is attached to the flutedplate 1101. This arrangement 1120 is schematically illustrated in FIG.11B. Attachment of optical films to the prismatic surface of abrightness enhancing layer is further described in U.S. Pat. No.6,846,089 (Stevenson et al.), incorporated herein by reference.

An exemplary embodiment illustrating an arrangement 1200 in which one ormore films are attached to the lower layer of the fluted plate isschematically illustrated in FIG. 12A. In this embodiment, a reflectivepolarizer 1210 is attached to the second layer 1204 of the fluted plate1201, and a prismatic brightness enhancing layer 1212 is attached to thefirst layer of the fluted plate 1201. An optional diffuser layer 1214may be attached to the lower surface of the reflective polarizer 1210.In other embodiments, the fluted plate itself may provide somediffusion. In such a case, it may be desired that the fluted plate 1201does not significantly depolarize the light that has passed through thereflective polarizer 1210.

Another exemplary embodiment 1220 of a fluted plate 1201 attached to anarrangement of light management films is schematically illustrated inFIG. 12B. In this embodiment 1220, a diffuser layer 1222 is attached tothe fluted plate 1201. An intermediate layer 1224 is disposed on thediffuser layer 1222 and a prismatic brightness enhancing layer 1226 isdisposed over the intermediate layer 1224. The diffuser layer 1222 maybe, for example, an acrylic foam tape: the foam tape deforms when theintermediate layer 1224 is pushed into the foam tape, creating arecessed region that the intermediate layer sits in. The intermediatelayer 1224 may have an optical function: for example, the intermediatelayer 1224 may be a reflective polarizer film. Examples of othersuitable arrangements of light management films that may be used with afluted plate are described in further detail in U.S. application Ser.No. 11/244,666, “LIQUID CRYSTAL DISPLAYS WITH LAMINATED DIFFUSERPLATES”, Docket No. 60107US003, filed on Oct. 6, 2005 and incorporatedherein by reference.

In addition to molding, there exist other methods of manufacturing afluted plate. One method is to attach a spine, that has connectingmembers already applied, to another optical film. This approach isschematically illustrated in FIGS. 13A and 13B. The spine 1302 has across member 1304 and an array of connecting members 1306. Theconnecting members 1306 may be integrated with the cross member 1304.For example, the spine 1302 may be formed by molding or extrusion. Thespine 1302 may be formed from the same types of materials as discussedearlier for a fluted plate. Thus, the spine 1302 may be formed ofoptically transparent or optically scattering material.

An optical film 1310 is attached to the connecting members 1306. Theoptical film may be any suitable type of film. For example, the film1310 may be a prismatic brightness enhancing film, a diffuser film, areflective polarizer film, a gain diffuser film, a lens film, anabsorbing polarizer, a matte film or the like. In addition, the opticalfilm 1310 may simply be a transparent film. Furthermore, optical filmsmay also be attached to the spine 1302 below the cross member 1304.

FIG. 13B shows the optical film 1310 attached to the connecting members1306. The film 1310 may be attached to the connecting members using anysuitable method. For example, the lower surface 1312 of the film 1310and/or the tips 1314 of the connecting members 1306 may be applied withan adhesive which is cured after the lower surface 1312 and theconnecting member tips 1314 are placed in contact. In another approach,in which the film 1310 and connecting members 1306 are both formed ofpolymeric materials, the film 1310 and connecting members 1306 may beplaced in contact before the respective polymeric materials have beenfully cross-linked, and the film 1310 and connecting members 1306 aresubsequently cross-linked together. Some other approaches may be used,for example contacting the optical film to the molten polymerimmediately following extrusion to create a bond between the opticalfilm and the flutes. In another approach, the flutes may be heated (postextrusion) and laminated at a later time. Also, a coextruded flute mayalso be employed whereby the flute is formed of one material as thematrix (non adhesive, structural member) with another materialcoextruded on the tip (adhesive type material).

After the film 1310 has been attached, the film 1310 and spine 1302together form a plate having flutes 1316.

In another embodiment, schematically illustrated in FIG. 14A (elementsseparated) and 14B (elements attached together), a spine 1402 has setsof connecting members 1406 a, 1406 b on respective sides of a crossmember 1404. Two optical films 1410 a, 1410 b may be attached to therespective sets of the connecting members 1406 a, 1406 b. The opticalfilms 1406 a, 1406 b may be any desired type of optical film, such as atransparent film, a diffuser film, a prismatic brightness enhancingfilm, a reflective polarizing film or the like.

After at least one of the films 1410 a, 1410 b has been attached to thespine 1402, the films 1410 a and 1410 b and spine 1402 together form aplate having flutes 1416.

One particular embodiment of an arrangement 1500 of optical films thatincludes a spine 1502 of the type illustrated in FIG. 14B, isschematically illustrated in FIG. 15. In this embodiment, a diffuserlayer 1510 is attached to the lower connecting members 1506 b and aprismatic brightness enhancing layer 1512 is attached to the upperconnecting members. A reflective polarizer layer 1514 may optionally beattached to the structured side of the prismatic brightness enhancinglayer 1512.

Another illustrative arrangement 1600 is schematically illustrated inFIG. 16, in which the reflective polarizer 1514 is positioned betweenthe diffuser layer 1510 and the spine 1502.

Another approach for attaching two layers together is to use layers thatare interconnectable. For example, the two layers may be mechanicallyattachable to each other using an attaching mechanism like that used toseal food storage bags. An exemplary embodiment of such a mechanism isillustrated in FIG. 17, which shows parts of the upper and lower layers1702, 1704. Each layer 1702, 1704 has respective interconnecting members1706, 1708 that are directed to the other layer. When the two layers1702, 1704 are pressed together, the interconnecting members 1706, 1708lock together to form the connecting members. The layers 1702, 1704 withrespective interconnecting members 1706, 1708 may be formed, forexample, using an extrusion process. The interconnecting members 1706may be, but are not required to be, of the same shape as theinterconnecting members 1708.

Whether or not spines are used to connect the upper and lower layers,the fluted plate may be formed in a partially continuous process. Thefilms forming the upper and lower layers, and the optional spine, may betaken off respective rolls and attached together. Once the layers areattached to one another, the resulting fluted product is relativelystiff. Individual plates can be cut from the continuous fluted product.

A fluted plate may be used to improve thermal management in a displaysystem, such as a television display or monitor. An exemplary embodimentof display system 1800, schematically illustrated in FIG. 18, includesone or more light sources 1802, a fluted plate 1804, an arrangement oflight management layers 1806, and a display panel 1808. A coolant mayflow through the flutes of the fluted plate 1804, which results in alower operating temperature of the display system. The coolant may beair and, in some embodiments, the air may flow through verticallyoriented flutes due simply to natural convection. In other embodiments,the coolant may be forced through the flutes by a coolant circulator.For example, a fan 1810 may be used to force air through the flutes ofthe fluted plate 1804. In other embodiments, a transparent fluid, suchas water, may be forced through the flutes by a pump.

It will be appreciated that there are many different possiblearrangement within the scope of the invention, in which different layersappear in different orders from bottom to top of the arrangement, or indifferent positions relative to the spine.

The present invention should not be considered limited to the particularexamples described above, but rather should be understood to cover allaspects of the invention as fairly set out in the attached claims.Various modifications, equivalent processes, as well as numerousstructures to which the present invention may be applicable will bereadily apparent to those of skill in the art to which the presentinvention is directed upon review of the present specification. Forexample, free standing optical films may also be used within a displaydevice alongside a fluted plate that is attached with other opticallayers. Also, a display may use more than one fluted plate. The flutesof the multiple fluted plates may be arranged parallel to each other, orthe flutes of one plate may be oriented non-parallel to the flutes ofanother fluted plate. The claims are intended to cover suchmodifications and devices.

1. A display system, comprising: a light source; a display panel; and anarrangement of light management layers disposed between the light sourceand the display panel so that the light source illuminates the displaypanel through the arrangement of light management layers, thearrangement of light management layers comprising a fluted plate, thefluted plate comprising a front layer facing the display panel, a backlayer facing the light source and a plurality of connecting membersconnecting the front and back layers.
 2. A system as recited in claim 1,wherein the arrangement of light management layers comprises at leastone of a reflective polarizer layer, a diffuser layer, and a prismaticbrightness enhancement layer.
 3. A system as recited in claim 1, whereinat least a portion of the fluted plate is formed of a diffusingmaterial.
 4. A system as recited in claim 1, further comprising at leastone light management layer attached to the fluted plate.
 5. A system asrecited in claim 4, wherein the at least one light management layercomprises at least one of a diffuser layer, a reflecting polarizerlayer, and a prismatic brightness enhancing layer.
 6. A system asrecited in claim 1, wherein at least one of the front and back layerscomprises a first light management layer.
 7. A system as recited inclaim 6, wherein the first light management layer comprises at least oneof a prismatic brightness enhancing layer, a diffuser layer, and areflective polarizer layer.
 8. A system as recited in claim 6, whereinthe connecting members comprise first and second connecting members, thefirst connecting members being attached to a cross member and connectingto the front layer, the second connecting members being attached to thecross member and connecting to the back layer, the first lightmanagement layer being attached to one of the first connecting membersand the second connecting members, and further comprising a second lightmanagement layer connected to the other of the first connecting membersand the second connecting members.
 9. A system as recited in claim 1,further comprising a controller coupled to control an image displayed bythe display panel.
 10. A system as recited in claim 1, wherein thedisplay panel comprises a liquid crystal display (LCD).
 11. A system asrecited in claim 1, further comprising a coolant circulator for forcinga cooling medium through flutes of the fluted plate.
 12. A system asrecited in claim 11, wherein the coolant circulator is a fan and thecoolant is air.
 13. A system as recited in claim 1, wherein flutes ofthe fluted plate are arranged vertically to permit natural convectivepassage of air therethrough.
 14. A system as recited in claim 1, whereinthe connecting members comprise first connecting members attached to thefront layer and second connecting members attached to the back layer,the first connecting members interlocking with the second connectingmembers.
 15. A light management unit for use between a display panel anda backlight, the light management unit having a display panel side fororienting towards the display panel and a backlight side for orientingtowards the backlight, the unit comprising: a fluted layer comprising afirst light management layer, a cross member substantially parallel to,and spaced apart from, the first light management layer and anarrangement of first connecting members integral with the cross member,the first connecting members attached to the first light managementlayer.
 16. A unit as recited in claim 15, wherein the first lightmanagement layer comprises one of a diffuser layer, a brightnessenhancing layer, and a reflective polarizer layer.
 17. A unit as recitedin claim 15, further comprising a second light management layer attachedto the fluted layer.
 18. A unit as recited in claim 17, wherein anarrangement of second connecting members connects the second lightmanagement layer and the cross member.
 19. A unit as recited in claim17, wherein the second light management layer is connected to the firstlight management layer so that the first light management layer liesbetween the cross member and the second light management layer.
 20. Aunit as recited in claim 15, wherein the first connecting members aredisposed on a display panel side of the cross member and extending fromthe cross member, the unit further comprising second connecting membersdisposed on a backlight side of the cross member, the second connectingmembers extending from the cross member, and further comprising a secondlight management layer attached to the second connecting members.